This commit closes: #145
The dependency format "pkg:arch" (e.g. "python3:any") was not well
parsed if not any version is given. This commit splits the dependency
name and architecture in all cases.
When `-dep-follow-all-variants` option is enabled, dependency resolving
process shouldn't stop even if dependency is already satisfied - there
mgiht be other ways to satisfy dependency.
Also fix issue with parsing multiarch specs like
`python:any`.
